Improving color stability of alkyl phenols



United States Patent IMPROVING COLOR STABILITY OF ALKYL PHENOLS Herman I. Enos, Jr., Wilmington, DeL, assignor to Hercules Powder Company, Wilmington, DeL, a corporation of Delaware No Drawing. Application July 22, 1957 Serial No. 673,151

4 Claims. (Cl. 260624) This invention relates to the stabilization of alkyl phenols and is particularly directed to a process for improving the color stability of said compounds.

The alkyl phenols are normally light colored when freshly prepared but many of these compounds take on a definite discoloration when allowed to stand. This deterioration is particularly manifest in the case of the polyalkyl phenols, many of which are employed as antioxidants under conditions such that it is important that there be no change in color.

It is a general object of the invention to provide a process forimproving the color stability of alkyl phenols which normally tend to discolor on aging. A further object is to provide a process of the above character which can be employed eflfectively in the treatment of polyalkyl phenols, especially the compound 2,6-di-tertbutyl-4-methyl phenol which is particularly susceptible to yellowing on aging. I

In accordance with the invention, it has been discovered that the color stability of alkyl phenols which have a normal tendency to discolor can be vastly improve'd'by,

treating said alkyl phenols with a minor amount of an abietylamine derivative of the formula:

CHBCOOX RN\ CHzOOOX Example 1 In this example there is treated according to the invention white crystals of 2,6-di-tert-butyl-4-methyl phenol which had been prepared by the acid clay catalyzed alkylation of p-cresol followed by fractional distillation. Into a mixing vessel there was placed 528.8 parts of said alkyl phenol and 1.6 parts of N,N-bis (carboxymethyl)- dehydroabietylamine. The mixture was heated and stirred for one-half hour at 80 C., at which temperature the alkyl phenol was molten. The liquid mixture was then poured into an aluminum tray, allowed to crystallize and broken into small pieces. A portion of the alkyl phenol treated as above and an untreated control were stored in closed metal cans at room temperature. Samples were removed from the cans periodically and examined visually. Gardner color determinations were also made 2,877,273 Patented Mar. 10, 1959 on melts of each sample. The results of this storage test are as follows:

Samples of the same 2,6-di-tert-butyl-4-methyl phenol employed in Example 1 were mixed in molten form with 0.1% and 0.01%, respectively, of N,N-bis(carboxymethyl)dehydroabietylamine. The crystallized mixtures were placed along with the control in closed metal cans and stored in an oven at 40 C. for 42 days. Visual examination at the end 'of the storage period showed that the control had become deep yellow, almost Orange. 011 the other hand, the sample containing 0.1% of the specified amine showed no change and the sample containing 0.01% amine showed only a slight trace of yellow.

Example 3 In place of the N,N-bis(carboxymethyl)dehydroabietylamine employed in Example 1, other abietylamine derivatives we're employed in the procedure of Example 1 in the same amount relative to the 2,6-di-tert-butyl-4- methyl phenol. lowing:

Potassium salt of N,N-bis(carboxymethyl)tetra-hydroabietylamine Ammonium salt of N,N-bis(carboxymethyl)abietylamine Sodium salt of N,N-bis(carboxymethyl)dihydroabietylamine Improvement in the color stability of the alkyl phenol similar to that obtained in Example 1 was demonstrated.

The abietylamine derivatives useful in the invention are already known to the art and can be prepared, for instance, by reacting an amine of the formula RNH with an equal molar quantity of chloroacetic acid to form an intermediate compound having the formula:

which is then solubilized as a salt and further reacted with a second mole of chloroacetic acid in the form of an alkali metal (e. g., sodium, potassium or lithium) or ammonium salt to produce the corresponding salt of the desired compound from which the free acid can be obtained by acidification. In another method of preparing the compounds, a reactant of the formula:

CHzCHzOH C'HZCHZOH is oxidized to a dicarboxylic acid by heating in the presence of an alkali metal hydroxide. The compounds employed in the invention are solids of relatively high softening point which are soluble in many organic solvents and, in the form of alkali metal or ammonium salts, are also soluble in water.

The derivatives employed were the fol- Following is an illustration of the preparation of one of the abietylamine derivatives. The starting material in the preparation is dehydrogenated rosin amine which is predominantly dehydroabietyl amine.

Into a reaction vessel equipped with a stirrer, thermometer and reflux condenser there was charged 124 parts of dehydrogenated rosin amine followed by the addition of 42 parts of chloroacetic acid dissolved in approximately 90 parts of ethanol. An exothermic reaction occurred and the temperature rose to 65 C. At this stage, a solution prepared by dissolving 17 parts of sodium hydroxide in 26 parts of water was added over a period of 90 minutes with stirring while maintaining the temperature at 65 C. The alcohol in the reaction mixture was then removed by distillation by raising the reaction temperature to 95 C. The temperature was then held at 95 C. for four hours during which time the pH fell from 8 to 6. There was next added a solution of 26 parts of potassium hydroxide in 240 parts of water which resulted in a curdy solution of pH 8.

In a separate vessel a solution of potassium chloroacetate was prepared by adding a solution composed ofture at 65 C. The resulting mixture was then heated to 90 C. and held for four hours, giving a final pH of 6. The hot reaction mixture was then layered with an equal volume of benzene and acidified with stirring to pH 2 by the addition of 10% hydrochloric acid. Two layers separated cleanly and the lower brine layer was removed. The hot benzene solution was washed with hot water. The acid fraction was then separated from nonacidic material by transfer to a 1% potassium hydroxide solution and the clear aqueous solution result ing was washed with ether and then acidified to pH 2 as above in the presence of benzene. The benzene solution was separated and distilled leaving 140 parts of a solid product melting at 96-103 C. and having an acid number of 231. Analysis showed the product to be the N,N-bis(carboxymethyl) derivative of the dehydrogenated rosin amine.

The process of the invention can be practiced with good results on any alkyl phenol that has a tendency to discolor on aging. It is especially advantageous for use upon alkyl phenols having an alkyl group of 2 to 20 carbon atoms in the molecule. Exemplary of the alkyl phenols that can be treated are the various cresols, mand p-ethyl phenol, p-propyl phenol, p-isopropyl phenol, p-tert-butyl phenol, 2,4-dimethyl phenol, Z-methyl-4-tert-butyl phenol, 2-tert-butyl-4-methyl phenol, 2- methyl-4-dodecyl phenol, 2,4-di-tert-butyl phenol, 2,6-diethyl phenol, 2-methyl-6-tert-butyl phenol, 2,4,6-trimethyl phenol, 2,6-diethyl-4-methyl phenol, 2,6-di-n-propyl-4- methyl phenol, 2,4,6-triisopropyl phenol, 2,6-diethyl-4- tert-amyl phenol and 2,6-di-tert-butyl-4-methyl phenol. Particularly good results are obtained in the treatment of the polyalkylphenols. The latter are prepared by conventional processes, the most common method being to heat phenol or an alkylated phenol with an alkene in the presence of an acidic condensing agent such as sulfuric acid, phosphoric acid, hydrochloride, ferric chloride or an acid clay. In the alkylation, the alkene attaches to one or more of the carbon atoms of the vphenyl nucleus depending on the proportions of the reactants. Usually the desired polyalkyl phenol is recovered by distillation and is light in color but has a tendency to discolor in storage.

The process of the invention can be carried out by different manipulative procedures. Although other materials proposed in the art for stabilizing alkyl phenols require the presence of solvent for compatibility purposes, it is one of the advantages of the present invention that it can be practiced py simply mixing the abietylamine derivative with the alkyl phenol while the latter is in the liquid state, i. e., molten if the alkyl phenol is normally solid. The use of a solvent is not precluded, however, and the invention can be practiced by dissolving the abietylamine derivative and the alkyl phenol in a mutual solvent from which the treated alkyl phenol can be recovered by evaporation or crystallization. A1-

ternatively, the alkyl phenol can simply be washed with a solution of the abietylamine derivative.

The amount of abietylamine derivative to be employed can be widely varied. As shown by the examples, amounts of abietylamine derivative as small as about 0.01% based on the alkyl phenol are beneficial although it is most often preferred to employ an amount of abietylamine derivative at least equal to about 0.05%. Considerably larger amounts, e. g., up to about 5%, of abietylamine derivative can, of course, be employed, although it is generally unnecessary to employ more than about 1% thereof.

The temperature at which the process of the invention can be carried out is also widely variable but a maximum temperature of about C. is recommended in order to avoid dealkyiation of the alkyl phenol. The lowest temperature employed in the case of alkyl phenols which are normally solid is the melting point of the alkyl phenol but in the case of normally liquid alkyl phenols, the temperature during the process can be as low as about 0 C.

It is an added benefit of the present invention that the abietylamine derivatives that are employed to stabilize the alkyl phenols are themselves effective rust and corrosion inhibitors. Consequently, an alkyl phenol containing one of the specified abietylamine derivatives has an enhanced ability to resist rust and corrosion in storage or use.

What I claim and desire to protect by Letters Patent alkyl phenol which tends to discolor on aging which comprises treating said alkyl phenol at a temperature within the range of about 0 C. to 125 C. with a minor amount within the range of about 0.01 to 5%, based on the weight of the said alkyl phenol, of an abietylamine derivative having the formula:

CHzCOOX OH2COOX in which R represents a radical selected from the group References Cited in the file of this patent UNITED STATES PATENTS Stevens et a1. Oct. 9, 1951 Manka Oct. 1, 1957 1. The process for improving the color stability of an, 

1. THE PROCESS FOR IMPROVING THE COLOR STABILITY OF AN ALKYL PHENOL WHICH TENDS TO DISCOLOR ON AGING WHICH COMPRISES TREATING SAID ALKYL PHENOL AT A TEMPERATURE WITHIN THE RANGE OF ABOUT 0* C. TO 125* C. WITH A MINOR AMOUNT WITHIN THE RANGE OF ABOUT 0.01 TO 5%, BASED ON THE WEIGHT OF THE SAID ALKYL PHENOL, OF AN ABIETYLAMINE DERIVATIVE HAVING THE FORMULA: 